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01/06/2017 - Twin Wins For Planetary Exploration

An artist’s conception of the Lucy spacecraft flying by the Trojan Eurybates — one of the six diverse and scientifically important Trojans asteroids to be studied. Right: Psyche, the first mission to a metal asteroid, will map features, structure, composition, and magnetic field, and examine a landscape unlike anything explored before. (Credit: SwRI and SSL/Peter Rubin)

The Psyche mission, a journey to a metal asteroid, has been selected for flight under NASA’s Discovery Program, a series of lower-cost, highly focused robotic space missions that are exploring the solar system.

Psyche includes prominent roles for Department of Earth, Atmospheric and Planetary Sciences (EAPS) professors Maria Zuber (leading the Gravity investigation), Richard Binzel (asteroid composition expert), and Benjamin Weiss (leading the Magnetometer investigation). Zuber and Binzel are also both member of MIT's Kavli Institute for Astrophysics and Space Research. The mission principal investigator is former EAPS professor Lindy Elkins-Tanton ’87, SM ’87, PhD ’02, now director of Arizona State University’s School of Earth and Space Exploration (SESE).

The mission’s spacecraft is expected to launch in 2023, arriving at the asteroid in 2030, where it will spend 20 months in orbit, mapping it and studying its properties.

“This mission, visiting the asteroid Psyche, will be the first time humans will ever be able to see a planetary core,” says Elkins-Tanton. “Having the Psyche mission selected for NASA’s Discovery Program will help us gain insights into the metal interior of all rocky planets in our solar system, including Earth.”

Psyche, an asteroid orbiting the sun between Mars and Jupiter, is made almost entirely of nickel-iron metal. As such, it offers a unique look into the violent collisions that created Earth and the other terrestrial planets.

The scientific goals of the Psyche mission are to understand the building blocks of planet formation and explore firsthand a wholly new and unexplored type of world. The mission team seeks to determine whether Psyche is a protoplanetary core, how old it is, whether it formed in similar ways to the Earth’s core, and what its surface is like.

"This is an opportunity to explore a new type of world — not one of rock or ice, but of metal," says Elkins-Tanton. "[The asteroid] 16 Psyche is the only known object of its kind in the solar system, and this is the only way humans will ever visit a core. We learn about inner space by visiting outer space."

Psyche — a window into planetary cores

Every world explored so far by humans (except gas giant planets such as Jupiter or Saturn) has a surface of ice or rock or a mixture of the two, but their cores are thought to be metallic. These cores, however, lie far below rocky mantles and crusts and are considered unreachable in our lifetimes.

Psyche, an asteroid that appears to be the exposed nickel-iron core of a protoplanet, one of the building blocks of the sun’s planetary system, may provide a window into those cores. The asteroid is most likely a survivor of violent space collisions, common when the solar system was forming.

Psyche follows an orbit in the outer part of the main asteroid belt, at an average distance from the sun of about 280 million miles, or three times farther from the sun than Earth. It is roughly the size of Massachusetts (about 130 miles in diameter) and dense (7,000 kilograms per cubic meter).

“Psyche's metallic nature has been tantalizing asteroid scientists for decades. It's a dream destination for new discoveries,” says Binzel.

Mission instrument payload

The spacecraft's instrument payload will include a magnetometer, multispectral imager, a gamma ray and neutron spectrometer, and a radio-science experiment.

The magnetometer experiment, led by MIT’s Benjamin Weiss and to be built by UCLA, is designed to detect and measure the remnant magnetic field of the asteroid. It’s composed of two identical high-sensitivity magnetic field sensors located at the middle and outer end of the boom. According to Weiss, “the goal of the magnetometer is to establish whether Psyche once generated a magnetic field, which would confirm that Psyche is the metallic core of a shattered protoplanet and teach us about how small bodies like asteroids and moons generate magnetism.”

The multispectral imager, which will be led by an ASU science team, will provide high-resolution images using filters to discriminate between Psyche's metallic and silicate constituents. It consists of a pair of identical cameras designed to acquire geologic, compositional, and topographic data.

The gamma ray and neutron spectrometer will detect, measure, and map Psyche's elemental composition. The instrument is mounted on a 7-foot (2-meter) boom to distance the sensors from background radiation created by energetic particles interacting with the spacecraft and to provide an unobstructed field of view. The science team for this instrument is based at the Applied Physics Laboratory at Johns Hopkins University.

The Psyche spacecraft will also use an X-band radio telecommunications system, whose team is led by MIT’s Maria Zuber and includes scientists at NASA’s Jet Propulsion Laboratory. This instrument will measure Psyche's gravity field which, when combined with topography derived from onboard imagery, will provide information on the interior structure of the asteroid. “This is an unprecedented opportunity to map the structure of the metallic core of a planetary body,” says Zuber. “The results will inform understanding of planetary accretion as well as the geodynamical processes that dominated differentiated planetary bodies in the earliest solar system.”

The Psyche mission team

In addition to Elkins-Tanton, ASU SESE scientists on the Psyche mission team include deputy principal investigator and co-investigator Jim Bell, co-investigator Erik Asphaug, and co-investigator David Williams.

NASA’s Jet Propulsion Laboratory managed by Caltech is the managing organization and will build the spacecraft with industry partner Space Systems Loral (SSL). JPL’s contribution to the Psyche mission team includes over 75 people, led by project manager Henry Stone, project scientist Carol Polanskey, project systems engineer David Oh, and deputy project manager Bob Mase. SSL contribution to the Psyche mission team includes over 50 people led by SEP Chassis deputy program manager Peter Lord and SEP Chassis program manager Steve Scott.

Twin wins

NASA also announced its selection of a second Discovery Program class mission that will perform the first reconnaissance of the Trojans, a population of primitive asteroids orbiting in tandem with Jupiter.

Called “Lucy,” the mission will launch in 2021 to study six of these exciting worlds. “This is a unique opportunity,” says Harold F. Levison, Lucy principal investigator from Southwest Research Institute in Boulder, Colorado. “Because the Trojans are remnants of the primordial material that formed the outer planets, they hold vital clues to deciphering the history of the solar system. Lucy, like the human fossil for which it is named, will revolutionize the understanding of our origins.”

“Understanding the causes of the differences between the Trojans will provide unique and critical knowledge of planetary origins, the source of volatiles and organics on the terrestrial planets, and the evolution of the planetary system as a whole,” says EAPS alumna Catherine Olkin ’88, PhD ’96, a Lucy deputy principal investigator now working at Southwest Research Institute.

Richard Binzel, who is also a member of the Lucy mission team says, of the twin announcements, “It's an amazing day to win on two missions. These distant Trojan asteroids may be hiding amazing clues for the chemistry of planets and life.”